It has been known to produce fibril cellulose from lignocellulosic fibres by the application of energy, which results in the fibrillation of the fibres. In this process, lignocellulosic fibres can be disintegrated into smaller parts by detaching fibrils which act as components in the fibre walls, wherein the particles obtained become significantly smaller in size. The properties of fibril cellulose thus obtained differ significantly from the properties of normal pulp. It is also possible to use fibril cellulose as an additive in papermaking and to increase the internal bond strength and tensile strength of the paper product, as well as to increase the compactness of the paper. Fibril cellulose also differs from pulp in its appearance, because it is gel-like material in which the fibrils are present in a water dispersion. Because of the properties of fibril cellulose, it has become a desired raw material, and products containing it would have several uses in industry, for example as an additive in various compositions.
Fibril cellulose can be isolated as such directly from the fermentation process of some bacteria (including Acetobacter xylinus). However, in view of large-scale production of fibril cellulose, the most promising potential raw material is raw material of plant origin and containing cellulose fibres, particularly wood. The production of fibril cellulose from wood raw material requires the decomposition of the fibres further to the size class of fibrils. In processing, a cellulose fibre suspension is passed several times through a homogenization step that generates high shear forces on the material. For example in U.S. Pat. No. 4,374,702, this is achieved by passing the suspension under high pressure repeatedly through a narrow gap where it achieves a high velocity, after which it impinges on an impact surface that decelerates the velocity. U.S. Pat. No. 4,481,077 discloses a method applying the homogenizer of said patent, wherein additives are admixed into the pulp before homogenization. The homogenization of fibre pulp consisting of a cellulose derivative, for the production of fibril cellulose is, in turn, known from U.S. Pat. No. 6,602,994.
In practice, compromises have to be made in the homogenization upon producing fibril cellulose: for good fibrillation, high input power/pulp flow rate is needed, which, in turn, decreases the productivity with the available homogenizer power. It is, for example, known to pass pulp several times through a homogenizer, to achieve a desired degree of fibrillation. Another problem with the processing of fibre-containing pulp is the susceptibility of homogenizers to clogging due to their structure, which may occur even at relatively low consistencies (1 to 2%), particularly if the starting pulp is not sufficiently well pre-processed. Attempts have been made to solve these problems, among other things, by reducing the fibre size in the starting pulp, for example by dry refining.